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9.17.2 Normal Scavem
R
G
Matrix
B
Scavem
action
Coring
Figure 9-26 Normal Scavem
With normal Scavem (as used in previous sets), the RGB
signals are added together and differentiated before they drive
the Scavem coil. The coring block prevents Scavem
processing from being performed on low signal levels.
9.17.3 Auto Scavem (Diagram SC)
R
Differen-
Matrix
G
tiator
B
2
I
C
Scavem
action
Clipper
(fixed)
Coring
Figure 9-27 Auto Scavem
The new Auto Scavem circuit (used in the EM5 chassis)
includes some extra blocks:
•
Clipper
•
Parabola modulation
Auto Scavem is fully software controlled by means of I
Auto TV algorithm controls the speed at which Auto Scavem is
adapted. This adaptation takes place together with the FBX
initialization, and takes about 1 second. The different circuit
stages are controlled via a DAC (item 7500, TDA8444.)
The new Auto Scavem circuitry also produces higher Scavem
currents, which results in sharper pictures. For the circuit
description, we split the circuit into eight stages.
Circuit Descriptions and Abbreviation List
Differen-
Output
Coring
tiator
stage
To
SVM
coil
No coring
Differentiator
slope
Transition
CL 16532149_088.eps
Coring
Clipper
Gain
Parabola
Output
modulation
Parabola
TDA8444
Reserved for
future use
Deflection
pulses
Differentiator
slope
Transition
Matrix and Differentiator
To
+12S
SVM
coil
Y_SCAVEM
(FROM SSB)
The 2fH RGB signals are added on the SSB (see diagram B4),
and presented to the emitter of transistor 7006.
131201
The next circuit is the differentiator. The combined signal
enters this circuit at the base of transistor 7008. The DAC7 line
controls the DC-level of this transistor, which is dependent of
the 'sharpness meter' reading in the Auto TV algorithm. By
means of this control signal, the voltage and capacity of varicap
diode 6000 is altered, which will adapt the differentiator.
The slope of the differentiator is controlled by this DC-level.
The differentiation itself is done by varicap diode 6000. Output
signal goes from the collector of transistor 7010 via emitter
follower (buffer) 7012, to the next stage.
Coring/Clipping and Gain
To
stage
SVM coil
2012
22n
SC6
2014
22n
DAC7 DAC5
CL 16532149_089.eps
131201
The coring circuit (items 7014 and 7016) prevents Auto
Scavem on the lowest signal levels (noise), while the clipper
circuit (items 7018 and 7020) always gives the same amount of
Scavem above a certain level.
The levels at which this occurs are controlled by the DAC4 and
DAC5 lines, and are dependent on the 'noise meter' reading in
the Auto TV program.
2
The input signal enters this circuit at emitter follower 7022, and
C. The
is strongly attenuated via voltage divider R3062 and R3064.
This is because the gain of transistor 7024 is set with the
adjustable voltage divider of R3066, R3068 and R3070. The
level at which this occurs is controlled by the DAC6 line, and is
dependent on the 'sharpness meter' reading in the Auto TV
program, the picture tube size, and the sharpness setting by
the customer.
EM5A NTSC
MATRIX
DIFFERENTIATOR
SC4
SC5
9V4
2008
8V 7
BF824
7V9
7008
7006
22n
BFS20
0V
2V6
1V 9
DAC7
Figure 9-28 Auto Scavem: Stage 1 and 2
CORING / CLIPPING
11V8
11V8
7018
BFS20
11V
BF824
7014
7022
BFS20
SC7
3062
2K2
2018
7016
0V8
RE S
10p
BFS20
0V
BF824
7020
0V
Figure 9-29 Auto Scavem: Stage 3 and 4
9.
EN 135
11V8
7012
BFS20
7V7
6V9
7010
BFS20
3 6000
1
BBY40
6002 1
3
BBY40
CL 26532041_082.eps
230402
GAIN
11V8
7026
DAC6
BFS20
6V9
SC8
6V2
7024
0V
BFS20
0V3
2020
22n
CL 16532149_091.eps
201201
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